During an observation period of 10 years 30 cases (11%) of twin transfusion syndrome were observed in a collective of 286 twin pregnancies at the University Women's Clinic Heidelberg. Typical symptoms of a twin transfusion syndrome as polyhydramnios, hydrops fetalis, polyserositis, disparity in fetal growth of the twins and pathological CTGs were examined for their diagnostic and prognostic values. A difference in birth weight of more than 25% was noted in only 28% of cases (range 2-58). A polyhydramnios was diagnosed in 63% of cases, an acute form in 30%. Eight of the nine pregnancies with an acute hydramnios ended in an abortion or intrauterine death up to 28 weeks of gestation. Amniocentesis for reduction of the excessive amount of amniotic fluid had no positive therapeutic effect. Eight of the pregnancies, in which a hydramnios had been detected, were further complicated by a hydrops fetalis (23%). Typical sinusoidal CTGs were registered in only 3 cases. Intrauterine fetal mortality respectively abortion up to 28 weeks of gestation was noted in 6 patients (12/60; 20%). Fetal mortality after 28 weeks of gestation occurred in 9/60 cases (15%). Four infants died more than 7 days post partum (7%). The fetal malformation rate was determined in our collective with 7% (4/60 fetuses). No chromosomal abnormalities were observed. The data collected show the prognostic relevance of the parameters analysed and reveal the cases in which a therapy might be effective. Ultrasonographic scanning of fetal activity or doppler flow measurements are further diagnostic procedures that can be employed in surveillance of risk pregnancies with twin transfusion syndrome. Also umbilical cord puncturing under direct ultrasonographic monitoring is of certain diagnostic and therapeutic value.